The Shema's opening line "Shema Yisrael Adonai Elohenu Adonai Echad" means "Hear O Israel, YHVH..." [yod, hey, vav, hey - the unspeakable name HaShem or the LORD or the Eternal One spoken as Adonai] ...is our God, YHVH [the LORD or Adonai] is One."
The rest of the prayer consist of quotations from Deuteronomy [ 6:4, 6:4-9, 11: 13-21], and Numbers [15: 37-41] alluding to the good that will come to us if we obey God's commandments. The opening line expresses the essence of monotheistic Judaism: the Shema is in contrast to pagan Romano-Hellenism's polytheism, pantheism and Christianity.
The latter stresses the Trinity which affirms the three-in-one idea: God the Father, God the Son, and God the Holy Spirit. According to Louis Jacobs (The Jewish Religion: A Companion 1995: 462] in Christian theologies, the three names of the Christian God can be interpreted as YHVH, Elohim, and Adonai....
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